The sea lamprey (Petromyzon marinus)
The sea lamprey doesn't look like a fish at all! In fact, this primitive fish doesn't even have bones. The sea lamprey has a long, slender eel-like body, with a sucker disc mouth. This parasitic fish attaches its mouth onto unsuspecting victims such as lake trout or whitefish, and literally sucks the life out of them! Since its introduction into the Great Lakes in the 1930's, this species has caused many problems for the commercial and recreational fishing industries and some 10 million dollars are spent each year to control them.